An image forming apparatus such as a printer and a copier includes a developing device, which uses developer to develop electrostatic latent images, a container for supplying developer to the developing device, and a main housing, in which the developing device and the container are stored. While the image forming apparatus forms images, an amount of the developer remaining in the container is not visually recognized because the container is stored in the main housing. Accordingly, the amount of the developer remaining in the container is typically detected by a magnetic permeability sensor JP 2008-52015 A.
A container disclosed in JP 2008-52015 A includes a magnetic permeability sensor, and a cleaning member, which cleans developer adhered to the magnetic permeability sensor. The magnetic permeability sensor may detect not only an amount of developer remaining in the container but also an amount of developer adhered to the cleaning member. Therefore, the container of JP 2008-52015 A may detect the amount of the developer remaining in the container with little influence of the developer adhered to the cleaning member.
While the image forming apparatus forms images, a condition of the developer in the container always changes. Therefore, the conditional change of the developer in the container may result in unstable determination of an amount of the developer remaining in the container. The techniques disclosed in JP 2008-52015 A do not contribute to identifying a state of the entire developer in the container although the techniques of JP 2008-52015 A may identify a state of the developer on the cleaning member.